In minimally invasive surgery, surgical tools and micro-surgical instruments are used in which the operator sees only a two-dimensional image of the surgical site and is therefore particularly dependent on his sense of touch. However, he cannot feel the tissue in the surgical area directly, but only indirectly, and therefore has to rely on endoscopes or laparoscopes that incorporate the surgical tool at the end of a shaft. It is possible in this context to use grippers, forceps or scissors with movable members as surgical tools.
To avoid damaging tissue as a result of excessive force impact, such instruments can provide the operator with feedback via the force being applied (force feedback). Such instruments are essentially operated purely mechanically; that is, the force that the operator exerts on the actuation device is conducted via Bowden cables or push rods to the surgical tool via the shaft. Gearboxes are often provided on the tool and/or on the handle for force or torque conversion. As a rule, however, these gearboxes do not have a linear transmission ratio, and consequently the operator grips tissues of varying thickness with a different force, even when the actuation force is the same. In addition, friction losses, which occur in the gearbox and especially on the diverted paths of Bowden cables, make the instrument sluggish, sometimes causing tasks to be fatiguing.
Therefore micro-surgical instruments have been developed with hydraulic actuation that comprise lower losses in force transmission from the actuation device to the tool than those with mechanical transmission.
Thus patent DE 195 37 897 A1,for instance, describes an endoscopic instrument on whose distal end of a shaft various surgical tools are disposed. Here the individual surgical tools can be brought into an operating position by a hydraulic actuator, whereas the others remain in resting position. However, the hydraulic actuator, such as a piston-cylinder arrangement, does not actuate the surgical tool directly but only moves it into the operating position. Therefore many lines must be fed through the shaft, unnecessarily increasing the structural size of the instrument.
In addition, patent DE 41 36 861 C2 discloses a micro-surgical instrument that includes a surgical tool that is pivotably disposed at the distal end of the shaft. The surgical tool can be operated by means of a handgrip, such that the force or signal transmission for operating the surgical tool occurs via control cables electrically, hydraulically or pneumatically. Hydraulic actuation of the surgical tool is not described there in any further detail.
In addition, patent DE 27 59 488 C2 describes a surgical instrument with hydraulically actuated tool of the same structural type, in which the tool is actuated by a hydraulic cylinder whose piston is coupled with a relay lever, which in turn acts on the members of the tool. The hydraulic cylinder can be impacted with pressure by means of a pressure-generating cylinder in the handgrip. The instrument disclosed in the patent comprises a number of parts, which are produced with some complexity and expense, and because of the many hydraulic connections and displaced cylinder linings, there is a constant risk of leakages
Finally, patent DE 35 23 022 A1 also discloses a surgical instrument of known structural type, in which a scissors is hinged at the outermost point of the shaft, so that it can open contrary to the insertion direction of the shaft. The scissors is actuated by sliding the shaft interior opposite to the shaft exterior by means of the handgrip. Actuation can also occur hydraulically, but this option is not described in any detail.